Grand Cherokee 4WD V8-4.7L (2003)
HEADLAMP SWITCH
The headlight switch on WJ vehicles uses a multiplexed (MUX) circuit to the BCM. The BCM will then control the park lamp, low/high head lamp
and fog lamp relay's based on this input.
FOG LAMP CONTROL
The body control module controls the operation of the fog lamp relay which controls the fog lamps. The fog lamps can only be on if the park or low
beam headlamps are on. If the high beams are turned on, the fog lamps will automatically be turned off.
Heating & A/C System
HEATING & A/C SYSTEM
SYSTEM AVAILABILITY
-
Depending on the model, either a Manual Temperature Control (MTC) or Automatic Zone Control (AZC) HVAC system is available in these
vehicles.
SYSTEM CONTROLS
Manual Temperature Control (MTC)
-
Refer to MTC system description and operation information.
The Automatic Zone Control (AZC) Module:
-
is fully addressable with the DRBIII.
-
communicates over the Programmable Communication Interface Multiplex System (PCI) Bus.
-
has dual infrared sensors, mounted in the AZC module face, which independently measure surface temperature to maintain occupant comfort
levels.
-
has dual-zone temperature-controls to provide a wide side-to-side variation in temperature to meet the needs of either front seat occupant.
-
can be operated in a manual mode.
-
uses engine temperature data, received over the PCI Bus, for cold engine blower lock-out.
-
uses engine RPM data, received over the PCI Bus, for wide-open throttle A/C cut-out.
-
uses vehicle speed data, received over the PCI Bus, to determine air-flow over the condenser for optimum cooling performance.
-
uses Ambient Temperature Sensor data, received over the PCI Bus, to optimize comfort control.
-
provides an A/C request to the BCM when compressor operation is desired.
-
provides a request to the BCM when rear defogger operation is desired.
-
controls fan speed, providing 10 blower speeds in manual mode and infinite speeds in automatic mode.
-
The Blower Motor Controller provides a 5.0 volt signal to the AZC Module over the Blower Motor Control circuit. The AZC Module
provides a variable duty cycle ground to the 5.0 volt signal based on input from the blower switch. When the blower switch is set to LO speed,
the AZC Module provides a short duty cycle (less time grounding the signal voltage). As higher blower speeds are requested, the AZC Module
increases the duty cycle (more time grounding the signal voltage). When the blower switch reaches HI speed, the duty cycle increases to where
the signal pattern is almost a flat line (with brief voltage spikes).
-
controls electronic door actuator operation.
-
A simplified control system for operation of the mode, recirculation, and temperature control actuators provides positive positioning without
the complexity of feedback from position sensors. The AZC Module knows the number of operating actuator revolutions required for full door
travel as well as the number of actuator commutator pulses per revolution. Using these parameters, the AZC Module runs the actuator for the
number of commutator pulses that correspond to the desired door position. To maintain accuracy, the system recalibrates itself periodically at
known zero and full travel conditions.
-
Refer to AZC system description and operation information.
The Body Control Module:
-
uses Evaporator Temperature Sensor data to prevent evaporator freeze up while maintaining optimum cooling performance.
-
controls rear defogger operation.
The Dual-Zone AZC HVAC system uses:
-
two, two-wire electronic blend door actuators.
-
one, two-wire electronic mode door actuator.
-
one, two-wire electronic recirculation door actuator.
SYSTEM REVISIONS
The 2003 WJ/WG HVAC systems remain mostly carryover from 2002. However, the 2003 model year AZC Module is NOT interchangeable with
other model year AZC Modules due to revised control software.
SYSTEM DIAGNOSTICS (MTC)
Fault detection is through Diagnostic Trouble Codes (DTCs)
-
DTCs are displayed by the DRBIII.
-
DTCs pertaining to the Evaporator Temperature Sensor are stored in the BCM. Diagnostics for these DTCs can be found in the Heating & A/C.
